Batteries are generally well understood devices that convert stored chemical energy into electrical energy. With changes in electronics and power requirements such as changes from analog to digital loads, battery technology is ever evolving and improving technically in chemistry, process control, material and control electronics. With the proliferation of digital electronics and wireless communications, batteries are becoming increasingly vital in modern technology. In many cases, the battery is the limiting factor for the size, shape and run time (or life) of the device which it serves.
Batteries have a limited lifetime, which is nonlinearly related to the chemical composition, application, environmental factors, and use/maintenance. Because batteries are a consumable, it is understood that battery performance declines over the lifetime until the battery eventually stops working. A problem lies in identifying when the battery will stop working, in advance of such a failure. This is vital, especially in critical applications that are dependant on battery power. For example, factories or even hospitals that require battery power cannot afford battery failure in certain applications.
Voltage measurement is commonly used to determine the state of a battery. When the measured voltage is below a predetermined threshold value, the battery is considered to be at or near the end of the battery lifetime and is replaced. While this is a simple measurement technique, it suffers from many disadvantages. For example, the battery must be charged prior to testing. If the battery is not fully charged, an incorrect determination that the battery requires changing is made. Further, this measurement does not estimate lifetime of the battery and does not consider load conditions during use or the pattern of use of the battery.
In another prior art battery testing method, a known load is applied to a battery while the voltage discharge is measured and used as an indication of battery state. This method requires that the battery be taken out of service for testing and charged prior to testing. Further, this test does not accurately reflect the load conditions during use and pattern of use of the battery, thereby resulting in inaccurate or unreliable results.
Other prior art systems use Electrochemical Impedance Spectroscopy (EIS) in conjunction with trending software to monitor the battery chemistry. Regular maintenance of battery systems (ie telecomm UPS systems) includes the use of an EIS device to quantify the state of the battery. These prior art systems for estimating the state of batteries suffer many disadvantages. For example, many systems estimate battery lifetime without consideration of the application, the load conditions during use or the pattern of use. Thus, the estimated lifetime is inaccurate or unreliable.
A better system and technique for estimating the state of a battery and an estimated lifetime is therefore desirable.